Protists that have a pellicle are surrounded by
silica dioxide
calcium carbonate
carbohydrates
proteins

proteins

Explanation:

Protists are unicellular eukaryotic organisms. As eukaryotes, they carry an individualized, delimited nucleus and well-defined cytoplasmic organelles. The Protista kingdom is made up of protozoa and certain unicellular algae. Among the protists that have a pellicle, such as Euglena, there is the presence of protein film organized spirally around the cytoplasm. This film is very flexible and allows the constant change of the shape of these organisms. These organisms are found in freshwater puddles with a lot of organic matter and are considered bioindicators of pollution in this kind of environment.

they float because they are less dense than the water itself

something denser than water, like a rock, will sink to the bottom

high growth (apex)